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Публикации по объекту
The Nainital-Cape Survey. III. A search for pulsational variability in chemically peculiar stars
Context: The Nainital-Cape survey is a dedicated research programme tosearch for and study the pulsational variability in chemically peculiarstars in the Northern Hemisphere. Aims: The aim of thesurvey is to search for such chemically peculiar stars that arepulsationally unstable. Methods: The observations of thesample stars were carried out in high-speed photometric mode using athree-channel fast photometer attached to the 1.04-m Sampurnanandtelescope at ARIES. Results: The new photometricobservations confirmed that the pulsational period of star HD 25515 is2.78-hrs. The repeated time-series observations of HD 113878 and HD118660 revealed that previously known frequencies are indeed present inthe new data sets. We have estimated the distances, absolute magnitudes,effective temperatures and luminosities of these stars. Their positionsin the H-R diagram indicate that HD 25515 and HD 118660 lie near themain-sequence while HD 113878 is an evolved star. We also present acatalogue of 61 stars classified as null results, along with thecorresponding 87 frequency spectra taken from 2002-2008. A statisticalanalysis of these null results shows, by comparison with past data, thatthe power of the noise in the light curves has slightly increased duringthe last few years.
| The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| The N2K Consortium. VII. Atmospheric Parameters of 1907 Metal-rich Stars: Finding Planet-Search Targets
We report high-precision atmospheric parameters for 1907 stars in theN2K low-resolution spectroscopic survey, designed to identify metal-richFGK dwarfs likely to harbor detectable planets. Of these stars, 284 arein the ideal temperature range for planet searches,Teff<=6000 K, and have a 10% or greater probability ofhosting planets based on their metallicities. The stars in thelow-resolution spectroscopic survey should eventually yield >60 newplanets, including 8-9 hot Jupiters. Short-period planets have alreadybeen discovered orbiting the survey targets HIP 14810 and HD 149143.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| The 78th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1706 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| The Nainital-Cape Survey. II. Report for pulsation in five chemically peculiar A-type stars and presentation of 140 null results
Aims.We search for photometric variability in chemically peculiar A typestars in the northern hemisphere. Methods: .High-speed photometricobservations of Ap and Am star candidates have been carried out fromARIES (Manora Peak, Nainital) using a three-channel fast photometerattached to the ARIES 104-cm Sampurnanand telescope. Results:.This paper presents three new variables: HD 113878, HD 118660 and HD207561. During the time span of the survey (1999 December to 2004January) pulsations of the δ Sct type were also found for the twoevolved Am stars HD 102480 and HD 98851, as reported in Joshi et al.(2002, 2003). Additionally, we present 140 null results of the surveyfor this time span. Conclusions: .The star HD 113878 pulsates witha period of 2.31 h, which is typical of δ Sct stars. HD 118660exhibits multi-periodic variability with a prominent period of nearly 1h. These periods need to be investigated and make HD 118660 aparticularly interesting target for further observations. For HD 207561,a star classified as Am, a probable pulsation with a period of 6 min wasfound in the light curves obtained on two consecutive nights. Both HD102480 and HD 98851 exhibit unusual alternating high and low amplitudemaxima, with a period ratio of 2:1. The analysis of the null resultsconfirms the photometric quality of the Nainital site.
| Studies of chemically peculiar stars
This thesis is on the framework of the "NainiTal-Cape Survey" programmefor searching photometric variability in chemically peculiar stars,initiated in 1997 at the ARIES, NainiTal, India, in collaboration withthe South African Astronomical Observatory, Cape Town and ISRO,Bangalore. This paper presents the corresponding results. The Am starsHD98851, HD102480, HD13079 and HD113878 were discovered to exhibit aScuti type of variability. Photometric variability was also discoveredin HD13038, for which the type of peculiarity and variability is not yetfully explained. The null results obtained in this survey are alsopresented and discussed, as they provide an interesting data referencefor upcoming studies.
| The Nainital-Cape Survey: A Search for Variability in Ap and Am Stars
The "Nainital-Cape Survey" program for searching photo-metricvariability in chemically peculiar (CP) stars was initiated in 1997 atARIES, Nainital. We present here the results obtained to date. The Amstars HD98851, HD102480, HD13079 and HD113878 were discovered to exhibitδ Scuti type variability. Photometric variability was alsodis-covered in HD13038, for which the type of peculiarity andvariability is not fully explained. The null results of this survey arealso presented and discussed.
| HD 8801: A Unique Single Am Star with γ Doradus and δ Scuti Pulsations
We have discovered the first example of a star pulsating intrinsicallywith both γ Doradus and δ Scuti frequencies. The star, HD8801, is an Am metallic-line star that appears to be single. Since thevast majority of Am stars are members of binary systems with periodsless than 1000 days and also do not pulsate, HD 8801 possesses a veryunusual, if not unique, combination of physical properties. Ourphotometry, acquired with an automatic telescope at FairbornObservatory, resolves six independent pulsation periods between 0.048and 0.404 days. The two longest periods lie within the range of γDor variables, while the four shorter periods are within the range ofδ Sct stars. Eleven radial velocities, obtained over an 11 monthperiod, have a mean of 0.8+/-0.3 km s-1, providing noevidence for a spectroscopic companion. The star is on the main sequenceand lies within both the γ Dor and δ Sct instability strips.Pulsation constants computed for the six periods agree with pulsationconstants computed for other γ Dor and δ Sct variables. HD8801 is also the first confirmed case of a metallic-line star pulsatingwith γ Dor frequencies. Its projected rotational velocity of 55 kms-1 is typical for Am stars, which, as a group, rotate moreslowly than normal A stars. HD 8801's slow rotation compared to normal Astars does not appear to arise from either a binary companion orevolutionary expansion and thus remains a puzzle. The coexistence ofmetallicism and pulsation in several main-sequence stars near the rededge of the δ Sct strip contradicts recent models that predictpulsations only in more evolved stars.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Discovery of unusual pulsations in the cool, evolved Am stars HD 98851 and HD 102480
The chemically peculiar (CP) stars HD 98851 and HD 102480 have beendiscovered to be unusual pulsators during the `Naini Tal-Cape Survey'programme to search for pulsational variability in CP stars. Time seriesphotometric and spectroscopic observations of these newly discoveredstars are reported here. Fourier analyses of the time series photometryreveal that HD 98851 is pulsating mainly with frequencies 0.208 and0.103 mHz, and HD 102480 is pulsating with frequencies 0.107, 0.156 and0.198 mHz. The frequency identifications are all subject to 1d-1 cycle count ambiguities. We have matched the observedlow-resolution spectra of HD 98851 and HD 102480 in the range 3500-7400Å with theoretical synthetic spectra using Kurucz models withsolar metallicity and a micro-turbulent velocity of 2 km s-1.These yield Teff= 7000 +/- 250 K, log g= 3.5 +/- 0.5 for HD98851 and Teff= 6750 +/- 250 K, log g= 3.0 +/- 0.5 for HD102480. We determined the equivalent H-line spectral class of thesestars to be F1 IV and F3 III/IV, respectively. A comparison of thelocation of HD 98851 and HD 102480 in the HR diagram with theoreticalstellar evolutionary tracks indicates that both stars are about1-Gyr-old, 2-Msolar stars that lie towards the red edge ofthe δ Sct instability strip. From comparison between the observedand calculated physical parameters, we conclude that HD 98851 and HD102480 are cool, evolved Am pulsators. The light curves of thesepulsating stars have alternating high and low amplitudes, nearlyharmonic (or subharmonic) period ratios, high pulsational overtones andAm spectral types. This is unusual for both Am and δ Sctpulsators, making these stars interesting objects for furtherobservational and theoretical studies.
| Discovery of pulsation in the Am Star HD 102480
Not Available
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Spectroscopic tests of photoelectric stellar classification of abnormal stars
Spectroscopic classification is obtained for 169 northern A5-G0 starspredicted by Olsen (1979, 1980) to have abnormal spectra on the basis ofStromgren four-color photometry. The success in identifying reddenedearly type stars was nearly 100 percent, for Am and early type weaklined stars about 75 percent, for stars above main sequence about 50percent, for composite spectra about 25 percent, and for Ap and LambdaBoo stars 0 percent. Thus photoelectric photometry is a successful firststep in discovering stars of the more extreme spectroscopicabnormalities.
| Estimation of spectral classifications for bright northern stars with interesting Stromgren indices
The purpose of this investigation is to provide spectroscopic observerswith finding lists of potentially interesting objects. From anunpublished UVBY catalogue of 7026 northern stars (mostly brighter than8.3m) 1094 objects with interesting combinations of UVBY indices havebeen selected. Most stars with post-HD classifications have beenexcluded, as well as late F dwarfs belonging to the intermediatepopulation II. For the 792 remaining stars estimated spectralclassifications are given. The techniques and experience from a previouspaper dealing with southern stars have been utilized here. Among thepredicted spectral classifications are 40 OB stars; 262 Ap, Am, or Fmstars; 16 supergiants of types A to G; 110 bright giants of types A to K(class II); 156 double stars or objects with composite spectra; 26 lateF dwarfs; 91 weak-lined dwarf and giant stars of types F to K, includingearly F-type population II field blue stragglers; and a few possiblefield horizontal branch stars, lambda Bootis-type stars, and late-typehalo giants.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Большая Медведица |
| Прямое восхождение: | 11h47m52.88s |
| Склонение: | +53°00'54.5" |
| Видимая звёздная величина: | 8.45 |
| Расстояние: | 239.808 парсек |
| Собственное движение RA: | 1.3 |
| Собственное движение Dec: | 2.5 |
| B-T magnitude: | 8.868 |
| V-T magnitude: | 8.485 |
Каталоги и обозначения:
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